1. Field of the Invention
The present invention relates to the separation of glycol di-alkyl ethers from the corresponding mono-ethers, especially to the preparation of high purity di-propylene glycol mono-tert-butyl ether (DPTB) by the separation of impurities such as di-propylene glycol di-tert-butyl ether (DE) from the DPTB.
2. Description of the Prior Art
Di-propylene glycol mono-tert-butyl ether (DPTB) is used commercially as a solvent and, in combination with dipropylene glycol as a concrete additive.
A commercial process for the production of DPTB involves reacting di-propylene glycol (DPG) with isobutylene over an acid ion exchange resin catalyst. A problem with such procedures is that certain amounts of di-propylene glycol di-tert-butyl ether are also produced which must be separated from DPTB prior to use of the DPTB as a concrete additive since the di-ether has a pronounced adverse effect in the usage in concrete.
Currently a costly and tedious extractive distillation technology involving the use of two columns and very large recycle streams is employed to accomplish the separation; see U.S. Pat. No. 5,552,024.
Various methods are known for separating minor amounts of impurities from various products including azeotropic and extractive distillation procedures but such prior methods are generally complicated and expensive. Steam stripping techniques have been employed but tend to result in the introduction of unwanted impurities with the steam, as well as producing waste water from condensing steam.
Now, in accordance with the present invention there is provided a simple and effective distillation procedure whereby the separation of impurities such as the di-ether from DPTB is achieved.